Grain refinement of aluminum alloy castings

ABSTRACT

THIS INVENTION RELATES TO A METHOD OF PRODUCING A FINER AND MORE EQUIAXED CAST GRAIN STRUCTURE IN ALUMINUM ALLOYS BY THE ADDITION OF THE DESIRED ALLOYING ELEMENT IN ITS PARTIALLY OR FULLY OXIDIZED STATE. ALUMINUM BASE ALLOYS AND ALUMINUM ALLOY ELECTRICAL CONDUCTORS PRODUCED BY THIS METHOD ARE ALSO DISCLOSED.

Aug. 6, 1974 E. c. CHIA GRAIN REFINEMENT OF ALUMINUM ALLOY CASTINGS 2 Sheets-Sheet 1 Filed Feb. 24. 1972 a 6. 1914 E. c. CHM 3,827,881

GRAIN REFINE-KENT OF ALUMINUM ALLOY CASTINGS Filed Feb. 24. 1972 2 SheetsSheet I nited States Patent 3,827,881 GRAIN REFINEMENT OF ALUMINUM ALLOY CASTINGS Enrique C. Chia, Carrollton, Ga., assignor to Southwire Company, Carrollton, Ga.

Filed Feb. 24, 1972, Ser. No. 228,824

Int. Cl. C22c 1/06 U.S..Cl. 75-138 7 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method of producing a finer and more equiaxed cast grain structure in aluminum alloys by the addition of the desired alloying element in its partially or fully oxidized state. Aluminum base alloys and aluminum alloy electrical conductors produced by this method are also disclosed.

SUMMARY OF THE INVENTION This invention discloses a method of refining the cast grain structure in aluminum alloys by the addition of the desired alloying element in the form of a metallic oxide. Metallic oxides suitable for addition to molten aluminum .within the scope of this invention are: Fe O and -Fe O One object of this invention is to produce a finer and more equiaxed cast grain structure in aluminum alloys.

Another object of this invention is to provide greater availability of nucleation sites during the alloying process.

Other objects and advantages of this invention will become apparent after reading the following description taken in conjunction with the accompanying photographs of the macrostructures.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1, 2 and 3 depict metallographic studies showing the cast grain structure of three ingots, designated as Samples 1, 2 and 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the structure of Sample 1 which is composed of unalloyed EC grade aluminum (99.45+% A1). The macrostructure shown in FIG. 1 is that of a columnar dendritic pattern which would normally be expected from the undisturbed supercooling of an aluminum ingot in the uninoculated condition.

FIG. 2 shows the structure of Sample 2 which is composed of 99.25 weight percent aluminum, containing small amounts of trace elements, which has been alloyed with 0.64 weight percent iron in the form of iron metal. The macrostructure shown in FIG. 2 is a columnar dendritic pattern similar to that of FIG. 1. The addition of 0.64 Weight percent iron metal has not provided nucleation sites for the ingot, and thus the structure has not been changed.

FIG. 3 shows the structure of Sample 3 which is composed of 99.20 Weight percent aluminum, containing small amounts of trace elements, which has been alloyed in situ with 0.64 weight percent iron by the addition of 0.91 weight percent ferric oxide, Fe O This resulted in the production of 0.58 weight percent aluminum oxide precipitate. The macrostructure depicted in FIG. 3 shows the array of fine, equiaxed grains which resulted from the availability of aluminum oxide nucleation sites.

The macrostructure in FIG. 3 shows evidence of the potent grain refining action of 0.58 weight percent aluminum oxide which has been freshly precipitated in the melt.

This melt was prepared by the addition of 0.91 weight percent ferric oxide, Fe O which produced an iron content of 0.64 weight percent. The added iron oxide quickly reacted with the molten aluminum by the thermit reaction to produce metallic iron and a very active form of freshly precipitated aluminum oxide. It is apparent from FIG. 3 that a very fine grained structure was produced by the freshly precipitated aluminum oxide.

The grain refining reaction occurs when the oxide of the alloying element is added to the molten aluminu and is reduced according to the formula:

where Fe is the alloying element, 0 is oxygen, Al is aluminum, and x and y are integers which are determined by the chemical formula of the oxide. In order for this reaction to occur, the metallic oxide, Fe O must be reducible in the presence of molten aluminum. Advantageous results have been achieved with the following metallic oxides: F203 and F6304.

The mechanism for refinement is the precipitation of fine particulate aluminum oxide in the alloyed molten aluminum. The aluminum oxide particles serve as nucleation sites for the subsequent formation of grains when the alloyed molten aluminum is supercooled below its solidification temperature during the casting.

Simultaneously with the reduction of the metallic oxide, Fe O and the formation of aluminum oxide, the elemental metal, Fe, is alloyed with the molten aluminum.

In accordance with this invention preferable results are obtained when the elemental metal is iron and when x=2 and y=3; or

x=3 and y=4;

according to the degree of oxidation of the iron.

When preparing the alloys of this invention the desired amount of metallic oxide to be added to the molten aluminum is arrived at by using the following formula, where Fe O designates the metallic oxide:

(2) (atomic Weight of Fe)=total metallic weight.

total oxygen weight total molecular weight of metallic oxide (y) (atomic weight of 0):

total metallic weight total molecular weight of metallic oxide =weight percent metal in the metallic oxide.

Thus, to get 0.64% Fe: =0.9l% Fe O The aluminum alloys of this invention can be produced as aluminum base alloys especially suited for producing high strength light weight products including rod, wire, cable, connectors, bus bars, receptacle plugs, other electrical contact devices and other articles of manufacture such as structural members, fasteners, automotive parts and the like; or can be formed into rod and wire having the required physical and electrical properties to be usable as electrical conductors.

After the preparation of a melt the aluminum alloy of this invention is preferably cast into a continuous bar. The cast bar is then hot-worked in substantially that condition in which it is received from the casting machine. A typical hot-working operation comprises rolling the bar in a rolling mill substantially immediately after being cast into the bar.

It should be understood that other methods of preparation may be employed to obtain suitable results. Other methods of preparation include conventional extrusion and hydrostatic extrusion to obtain bar, rod, or wire directly; sintering to obtain rod, billet, slab, bar or wire directly; casting rod, billet, slab, bar or wire directly from the molten aluminum alloy; and conventionally casting aluminum alloy billet, slab and bar which can subsequently be hot-worked to rod and drawn into Wire if desired.

Preferred embodiments of this invention include aluminum base alloys and aluminum alloy electrical conductors produced by the addition of Fe O or Pe o, to molten aluminum.

In accordance with this invention particularly advantageous results have been achieved with the following aluminum base alloys and aluminum alloy electrical conductors.

An aluminum base alloy consisting essentially of from about 0.30 to about 3.00 weight percent iron; no more than about 0.40 weight percent silicon; from about 0.005 to about 0.40 total weight percent of trace elements selected from the group consisting of vanadium, copper, manganese, magnesium, zinc, boron and titanium; and from about 96.20 to less than about 99.70 weight percent aluminum; said alloy having an iron to silicon ratio of about 2:1 or greater. This aluminum base alloy is produced by the addition of from about 0.43 to about 4.29 weight percent Fe O or by the addition of from about 0.42 to about 4.17 weight percent Fe O An aluminum alloy electrical conductor having a minimum conductivity of sixty-one percent (61%) IACS and consisting essentially of from about 0.45 to about 0.95 weight percent iron; no more than about 0.15 weight percent silicon; less than about 0.05 Weight percent each of trace elements selected from the group consisting of vanadium, copper, manganese, magnesium, Zinc, boron and titanium; and from about 98.95 to less than about 99.55 weight percent aluminum, said alloy containing no more than about 0.15 total weight percent trace elements and having an iron to silicon ratio of about 2:1 or greater. This aluminum alloy electrical conductor is produced by the addition of from about 0.64 to about 1.36 weight percent Fe O or by the addition of from about 0.62 to about 1.32 Weight percent Fe O The aluminum base alloys and aluminum alloy electrical conductors of this invention have very fine and equiaxed cast grain structure. This grain structure porduces a material having a higher tensile strength than alloys containing the same amount of alloying metal where the metal is added in its metallic state. The alloys of this invention also possess improved holding properties at high temperatures, i.e. when formed into a conductor the alloys of this invention retain a more positive contact with various connectors at higher temperatures than prior art alloys. During fabrication such as hot-rolling the equiaxed grain structure of these alloys deform more easily than prior art alloys, lessening the possibility of directional stress, thereby producing a more uniform structure.

A more complete understanding of the invention will be obtained from the following examples.

EXAMPLE NO. 1

A comparison between prior aluminum alloy wire alloyed with metal in the metallic state and the present aluminum alloy wire is provided by a prior art aluminumiron alloy with an aluminum content of 99.25 weight percent, iron content of 0.64 weight percent, silicon content of 0.059 weight percent, and trace amounts of typical impurities. The present alloy was prepared with aluminum content of 99.20 Weight percent, iron content of 0.64 weight percent, produced by the addition of 0.91% Fe O silicon content of 0.056 weight percent, and trace amounts of typical impurities. Both alloys were continuously cast into continuous bars and hot-rolled into continuous rod in similar fashion. The alloys were then cold-drawn through successively constructed dies to yield #12 AWG continuous wire. Sections of the wire were collected on separate bobbins and batch furnace-annealed at various temperatures for 3 hours time to yield sections of the prior art alloy and the present alloy of varying tensile strengths.

TABLE I Tensile strength Annealing tem- Prior art Present pcrature, degrees alloy alloy As shown in Table I, the present alloy has a surprisingly improved property of increased tensile strength over conventionally alloyed aluminum-iron alloys.

EXAMPLES 2 THROUGH 11 Twelve aluminum alloys were prepared with varying amounts of major constituents. Those alloys are reported in the following table:

TABLE II Example No.

Prior Percent art Present alloy alloy Al Fe Si TABLE I11 Conduc- Conductivity in tivity in I Example percent Tensile Example percent Tensile No. IACS strength No. IACS strength While the invention has been described in detail with particular reference to certain preferred embodiments, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as hereinbefore described and defined in the appended claims.

What is claimed is:

1. The method of refining the cast grain structure of aluminum alloys comprising adding to molten aluminum a metallic oxide selected from the group consisting of 'Fe O and Fe O and permitting the metallic oxide to react in situ with the molten aluminum to produce metallic metal which alloys with the molten aluminum, and freshly precipitated aluminum oxide which acts as an effective aluminum grain-refining agent.

2. The method of Claim 1 comprising adding a metallic oxide selected from the group consisting of Fe O and Fe O to molten aluminum having no more than about 0.40 weight percent silicon; from about 0.005 to about 0.40 total weight percent trace elements selected from the group consisting of vanadium, copper, manganese, magnesium, zinc, boron and titanium; from about 96.20 to less than about 99.70 weight percent aluminum; and having an iron to silicon ratio of about 2:1 or greater.

3. The method of Claim 2 comprising adding from about 0.43 to about 4.29 weight percent Fe O 4. The method of Claim 2 comprising adding from about 0.42 to about 4.17 weight percent Fe O 5. The method of refining the cast grain structure of an aluminum alloy conductor having a minimum conductivity of sixty-one percent (61%) IACS; no more than about 0.15 weight percent silicon; less than about 0.05 weight percent each of trace elements selected from the group consisting of vanadium, copper, manganese, magnesium, zinc, boron and titanium; and from about 98.95 to less than about 99.55 weight percent aluminum, said alloy containing no more than about 0.15 total weight percent trace elements and having an iron to silicon ratio of about 2:1 or greater; comprising adding a metallic oxide selected from the group consisting of Fe O and Fe O to the molten aluminum alloy.

6. The method of Claim 5 comprising adding from about 0.64 to about 1.36 weight percent Fe O 7. The method of Claim 5 comprising adding from about 0.62 to about 1.32 weight percent Fe O References Cited UNITED STATES PATENTS 3,607,241 9/1971 Bolling etal. 75-138 3,512,221 5/1970 Schoerner 75138 RICHARD o. DEAN, Primary Examiner US. 01. X.R. 75--68 R 

